The purpose of any paint spray booth is to evacuate the spent paint particulate and fumes from the point of paint application to an area where they may be removed from the air stream. In some instances this removal is for the benefit of the paint spraying operator, but is always beneficial to the painting process itself in that it is not desirable to have spent paint particulate re-deposited on the painted or to be painted surface. There have been acceptable standards established for air movement through the point of spray paint application. It is most desirable to maintain a constant approved air velocity whenever the paint spray booth is in operation. Unfortunately, in the case of present day dry filter spray booths, the air velocity through the point of paint application constantly diminishes as the dry filters continue to collect spent paint particulate. This diminishing performance may reach such a point of ineffective operation that the painting operation itself must cease until the clogged filters have been replaced with clean new filters. Additionally, there is a tendency to postpone the booth shutdown for filter replacement, thereby jeopardizing both the operator and finished product prior to shutdown. Further, as the filters begin to clog, their effectiveness because of increasing velocity through the ever diminishing unclogged filter area begins to pull particulate through the filter releasing it to the atmosphere. The booth down times to replace filters may have to be repeated anywhere from several hours to several days. The combined cost of production loss and replacement cost of filters becomes considerable.
In contrast, a water wash spray booth provides a constant non-diminishing air flow for a much longer period of time, consequently, having a high average performance during its operating cycle between shutdowns for sludge (accumulated spent paint) removal.
Paint spray booths have long used water as a means to wash out or entrain paint particulate or materials generated while spraying paint on an article being painted and into the surrounding air as overspray. In the water wash type booth a blower or fan is used to bring the surrounding air and paint overspray into a washer or eliminator section of the booth where this paint laddened air is cleaned or separated from the spent paint material, the latter eventually collection as sludge. Examples of this type of prior art booth may be found in Binks Manufacturing Company's U.S. Pat. No. 2,385,077. This type booth has long been used with acceptable results. However, increases in concerns as to air pollution, waste solids disposal and reductions in the amounts of materials which can be discharged both into the air and/or into solids disposal sites, makes improvements in this type of booth desirable so it can meet future air pollution and waste disposal requirements and to make them competitive and superior to dry filter booths.
The prior art water washed booths of this type usually had one or more water supply manifolds to generate in some cases a water curtain backstop to catch the overspray and one or more sheets of water spray to wash spent paint from the air in which it was entrained and also to keep the spent paint from building up on the interior structure, usually of sheetmetal, of the booth itself. In the prior art booths, as shown in U.S. Pat. No. 2,385,077, these prior water supply manifolds had a plurality of drilled holes spaced in rows extending the width of the booth or sometime had such holes tapped to receive small individual screwed in water nozzles. In U.S. Pat. No. 2,385,077 the prior art water manifold shown had the plurality of water sprays emanating from the row of holes covered by a concave curved cap, to generate a pair of opposed water spray sheets coming off the two or opposed edges of the cap. Alternatively, that patent also shows in FIG. 7 a water manifold having two rows of water spray holes generally about 180.degree. apart each covered by a curved cap in an inverted, convex relationship to generate four spray sheets, instead of two, two off of the edges of each curved cap. However, because the two rows of holes were arranged in a manner about 180.degree. apart, one at the top and the other at the bottom of the manifold, the water spray sheets apparently did not fully cover the surrounding sheetmetal of the booth by themselves, and a separate auxiliary water manifold was shown to provide additional covering water spray to prevent paint build up on the adjacent sheetmetal.
Other prior art booths of this type have used an angular, instead of a curved, cap over a single row of water nozzles as described above to generate two water sheets which generally fully cover the surrounding sheetmetal but generate less cleaning action than would the four water spray sheet forming structure. This type of prior art water manifold usually had water nozzles screwed into tapped holes in the pipe forming the manifold, and the holes in the manifold were covered by an angular cap, wherein the side edges of the angular cap were closer to the pipe (concave) than the center or juncture of its two angular sides. This construction had a tendency to plug or clog if the water being expelled from the nozzle was not relatively free of spent paint particulate. This plugging or clogging was usually due to spent paint materials being carried in the water from the water supply manifold which was sprayed out of the nozzles into the underside of the angular cap. While the clogging started usually on the underside of the angular cap, it would continue to build until it also plugged the nozzle. Due to the fact the nozzles' openings were covered by the cap and extended upwardly between the two angular sides of the cap, there was little or no room to clear away the clog. Thus, in many cases the clogging was ignored as it was difficult or impossible to clear, resulting in less efficient cleaning of the paint laddened air and build up of spent paint on the surrounding sheetmetal surfaces. Sometimes when clogging because severe and much of the length of the caps and or holes beneath them became clogged, the booth was just shut down and partially disassembled so that the manifold could be removed to be cleared, and then reinstalled. This procedure, of course, caused loss of operating time for the booth and increased maintenance expense, and less than maximum cleaning efficiency when the booth was operated with one or more clogged holes and or caps. It should be appreciated that when the holes or covering caps were clogged or had paint build up on them, the resulting water sheet sprays or falls off the caps may be imperfect and or have voids therein which would let more paint laddened air pass therethrough without being fully cleaned.
The prior art booths, such as shown in U.S. Pat. No. 2,385,077, also generally had a deep (one foot or so) water pan beneath the entire booth into which the water from a front water curtain and water manifold sheet sprays eventually collected. This front water curtain and sheet sprays water had spent paint particulate entrained therein, which was removed from the air flowing past the article being painted then collected by the water flowing in the booth. As the water from the curtain and water sheets carrying the entrained paint collected in the generally stagnant water pan, the entrained material tended to drop out or collect in the pan. If the entrained paint material was heavier than water, as was frequently the case, this spent paint settled into the bottom of the pan. If initially this entrained material was lighter, first it floated on the water in the pan and then agglomerated into heavier particles and eventually sank. This settling action was thought desired for booth operation. When sufficient settling occurred so that it seriously adversely affected painting operation, or just periodically, the booth was shut down and the settled spent paint material was usually hand shoveled out. Thus booth operating time was lost; there was difficult and bothersome hand labor and increased maintenance expense. Generally, in the past a heavily used booth of this type might have to be cleaned as frequently as twice a week and cleaning could take as long as eight hours or more. Further, as the pan extended under the entire booth, much of the spent paint collected in places under the booth that were very difficult to clean. Further, the difficulty in cleaning resulted in increased spent paint being carried out of the pan into the air washer means, water supply manifold, outlets and/or nozzles, resulting in the same and/or their covering caps being partially or fully clogged as discussed above.